TRS-80 DOS - NEWDOS/80 v2.0 for the Model III - SYS12/SYS Disassembled

SYS12/SYS

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NEWDOS/80 v2.0 SYS12/SYS Disassembly - REF (Model III)

SYS12/SYS carries out the Disk BASIC direct command REF, which lists where line numbers, variable names or a piece of text are used in the program. It loads 4D00H-51D2H in five load records (transfer address 4D00H); the code ends at 51B1H, 51B2H-51BEH are data and 51BFH-51D2H are 20 bytes of 00H. Its variables 51D3H-51FFH lie after the file. SYS18/SYS runs it from its command table (REF, code 2EH): at its 5531H it pushes BASIC/CMD's 641EH (the end of the statement) and does RST 28H. When REF is done SYS12/SYS returns through the SYS0/SYS dispatcher (4BC5H) to 641EH and then to the ROM's READY at 1A25H; a plain REF that finds a line jumps into the ROM's LIST at 2B33H instead, a bad parameter goes to the ROM's SYNTAX ERROR at 1997H, and 4F2BH is described below.

The page shows every byte of the file once, in address order.

The Forms of REF

The scan (4F46H) passes strings, REM and ' remarks, DATA statements, numbers with a fraction and constants after &H and &O; the AS of a FIELD statement in the same line is not taken as a name. A line with a match changes the JP Z,4DFCH at 4F6DH into JP 4DFCH, so the line is reported when the scan reaches the next one.

At 4F2BH a plain REF that walks past the last line of the program (no line after the last one shown) jumps to the Text End message with a line address still on the stack, so the RET at the end of BASIC 5D70H goes to that address, the program's end marker, and not back through the dispatcher.

Variables

ROM Addresses

DOS Addresses

BASIC/CMD Addresses

Operands and Opcodes Changed at Run Time

Variables After the File

Outside Routines

4D00H - REF: Read the Parameter

SYS18/SYS runs REF from its command table (the entry REF, code 2EH) at its 5531H: it pushes BASIC/CMD's 641EH (the end of the statement) above the ROM's READY entry 1A25H (pushed at its 5518H) and does RST 28H with Register A = 2EH (slot 0EH, function 1). The SYS0/SYS dispatcher calls 4D00H with Register Pair HL = the command line after REF; SYS12/SYS's RET goes back through the dispatcher (4BC5H) to 641EH. Forms, from the code: REF alone (list the next line that holds the remembered item), REF @n (the same from line n on), REF name or REF number (every line that uses it), REF "text or REF =text (every line holding the text), REF followed by the multiplication sign or $ (every line number and name in the program, in order; $ also prints), and either of those followed by a name or number (the full report from that item on).

4DB0H - The Full Report: the Next Item

Each round of the full report first scans the whole program in mode 0 for the smallest line number or name above the last one reported (51D3H), keeping the addresses of up to 32 lines that use it in the DOS sector buffer at 4300H; then it reports that item in mode 1. Line numbers come before names. Holding BREAK pauses between items (ENTER goes on), the up arrow stops the report.

4DFCH - At the Next Line

Reached through the JP at 4F6DH with Register Pair DE at the link field of the next line: always when the line just scanned had a match (4F6DH was made JP), otherwise only when the link's low byte is 00H. A line with a match is reported (4E80H); the end marker ends the scan.

4E80H - Report a Line

Reached from 4E01H with Register Pair DE at the next line's link field, after a line with a match. In mode 3 the line is listed. Otherwise the line's number (4E76H) is shown once for every form of use counted in it (51E5H-51EEH): the name alone, with $ % ! # (the type characters at 51B2H-51B5H), and each of these as an array (followed by an opening parenthesis), with the count when it is more than one. A line number or a text search has only the first counter.

4F07H - Plain REF and REF @n

Finds the first line after the last one shown (4E76H; FFFFH = from the first line, n - 1 after REF @n) and scans from there in mode 3 for the remembered item (or the search text), listing the first line that holds it.

4F46H - Scan the Text

Register Pair DE walks through the program's text. Strings, REM and ' remarks, DATA, constants after & and decimal fractions are passed; line numbers (strings of digits) and variable names are collected and compared with the item. A match counts in the counters 51E5H-51EEH and turns the JP Z,4DFCH at 4F6DH into JP 4DFCH, so that the line is reported when the scan reaches the next line. During a text search the JP 512FH at 4F7CH compares every byte with the search text instead.

5101H - Remember the Line

Adds the address of the line being scanned (4E7AH) to the list at 4300H-433FH (32 lines) unless the list is full or the line is already its last entry.

512FH - Text Search

Reached through JP 512FH at 4F7CH with Register A = the byte of the line at Register Pair DE. Compares the bytes from there with the search text at 51EFH up to its 00H end; a match counts in 51E5H, the scan goes on after it.

514BH - Small Helpers

514BH: the next byte of the line in Register A, passing spaces, 09H and 0AH. 515AH: the CARRY FLAG if Register A is not a letter or digit; 5161H: the CARRY FLAG if it is not a letter. 5168H and 516EH: store the best item's characters (Register Pair BC) and length byte, set 5021H and empty the line list; 5171H: only the last two.

5189H - Compare Characters

Compares Register C characters from 51E0H with those at Index Register IY. The Z FLAG is set if they are all equal (or Register C is 0); otherwise the flags of the first difference.

519BH - Position the Output

519EH displays a space; at column 53 or beyond it starts a new line, and near the start of a line it indents to column 7, past the item's column.

51B2H - Data

The type characters and the message of 4E20H.

51D3H - Variables After the File

Not loaded by SYS12/SYS (the file ends at 51D2H); they keep their contents while no other overlay overwrites them.